Copper(II) hypophosphite has been shown to exist as several polymorphs. The crystal structures of monoclinic α, orthorhombic β and orthorhombic γCu(H_{2}PO_{2})_{2} have been determined at different temperatures. The geometry of the hypophosphite anion in all three polymorphs is very close to the idealized one, with point symmetry mm2. Despite having different space groups, the structures of the α and βpolymorphs are very similar. The polymeric layers formed by the Cu atoms and the hypophosphite ions, which are identical in the α and βpolymorphs, stack in the third dimension in different ways. Each hypophosphite anion is coordinated to three Cu atoms. On cooling, a minimum amount of contraction was observed in the direction normal to the layers. The structure of the polymeric layers in the γpolymorph is quite different. There are two symmetryindependent hypophosphite anions; the first is coordinated to two Cu atoms, while the second is coordinated to four Cu atoms. In all three polymorphs, the Cu atoms are coordinated by six O atoms of six hypophosphite anions, forming tetragonal bipyramids; in the α and βpolymorphs, there are four short and two long Cu—O distances, while in the γpolymorph, there are four long and two short Cu—O distances.
Supporting information
Copper(II) hypophosphite was synthesized by adding hypophosphorous acid,
H_{3}PO_{2} (2.3771 g of 50% solution in 35 ml of water), to basic copper
carbonate, CuCO_{3}·Cu(OH)_{2} (1 g). The reaction mixture was evacuated
until carbon dioxide evolution had stopped (about 10 min). Crystals were grown
at 278 K from a solution in water under a nitrogen atmosphere. During crystal
growth, initial formation of crystals with a rhombic plate habit was observed.
The quantity of needle crystals can be increased by adding glycerinum and
increasing the temperature of the solution to 288 K.
In all three structures, the H atoms were located from a difference
electrondensity map. The positions of the H atoms in the α and
βpolymorphs were refined without constraints. The positions of H atoms in
γpolymorph were refined as CH_{2} groups with fixed O—P—H angles and free
P—H bond lengths.
Data collection: SMART (Siemens, 1994) for alpha270, alpha100, beta270, beta100; CAD4 Software (EnrafNonius, 1989) for gamma270. Cell refinement: SAINT (Siemens, 1994) for alpha270, alpha100, beta270, beta100; CAD4 Software for gamma270. Data reduction: SAINT for alpha270, alpha100, beta270, beta100; CAD4 Software for gamma270. For all compounds, program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Siemens, 1994); software used to prepare material for publication: SHELXL97.
Crystal data top
Cu(H_{2}PO_{2})_{2}  F(000) = 190 
M_{r} = 193.51  D_{x} = 2.696 Mg m^{−}^{3} 
Monoclinic, P2_{1}/c  Mo Kα radiation, λ = 0.71073 Å 
a = 7.2186 (1) Å  Cell parameters from 993 reflections 
b = 5.3462 (2) Å  θ = 2.9–29.1° 
c = 6.2521 (3) Å  µ = 5.14 mm^{−}^{1} 
β = 98.8352 (11)°  T = 270 K 
V = 238.42 (2) Å^{3}  Prism, blue 
Z = 2  0.19 × 0.11 × 0.03 mm 
Data collection top
Siemens SMART CCD diffractometer  620 independent reflections 
Radiation source: finefocus sealed tube  578 reflections with I > 2σ(I) 
Graphite monochromator  R_{int} = 0.034 
Detector resolution: 8.192 pixels mm^{1}  θ_{max} = 29.1°, θ_{min} = 2.9° 
ω scans  h = −7→9 
Absorption correction: analytical (XPREP; Siemens, 1995)  k = −7→7 
T_{min} = 0.521, T_{max} = 0.859  l = −8→8 
1697 measured reflections  
Refinement top
Refinement on F^{2}  Secondary atom site location: difference Fourier map 
Leastsquares matrix: full  Hydrogen site location: difference Fourier map 
R[F^{2} > 2σ(F^{2})] = 0.031  All Hatom parameters refined 
wR(F^{2}) = 0.068  w = 1/[σ^{2}(F_{o}^{2}) + (0.0273P)^{2} + 0.2371P] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
S = 1.18  (Δ/σ)_{max} < 0.001 
620 reflections  Δρ_{max} = 0.47 e Å^{−}^{3} 
43 parameters  Δρ_{min} = −0.36 e Å^{−}^{3} 
0 restraints  Extinction correction: SHELXL97, Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
Primary atom site location: structureinvariant direct methods  Extinction coefficient: 0.033 (5) 
Crystal data top
Cu(H_{2}PO_{2})_{2}  V = 238.42 (2) Å^{3} 
M_{r} = 193.51  Z = 2 
Monoclinic, P2_{1}/c  Mo Kα radiation 
a = 7.2186 (1) Å  µ = 5.14 mm^{−}^{1} 
b = 5.3462 (2) Å  T = 270 K 
c = 6.2521 (3) Å  0.19 × 0.11 × 0.03 mm 
β = 98.8352 (11)°  
Data collection top
Siemens SMART CCD diffractometer  620 independent reflections 
Absorption correction: analytical (XPREP; Siemens, 1995)  578 reflections with I > 2σ(I) 
T_{min} = 0.521, T_{max} = 0.859  R_{int} = 0.034 
1697 measured reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.031  0 restraints 
wR(F^{2}) = 0.068  All Hatom parameters refined 
S = 1.18  Δρ_{max} = 0.47 e Å^{−}^{3} 
620 reflections  Δρ_{min} = −0.36 e Å^{−}^{3} 
43 parameters  
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. 
Refinement. Refinement of F^{2} against ALL reflections. The weighted Rfactor
wR and goodness of fit S are based on F^{2}, conventional
Rfactors R are based on F, with F set to zero for
negative F^{2}. The threshold expression of F^{2} >
σ(F^{2}) is used only for calculating Rfactors(gt) etc.
and is not relevant to the choice of reflections for refinement.
Rfactors based on F^{2} are statistically about twice as large
as those based on F, and R factors based on ALL data will be
even larger. 
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  
Cu1  0.0000  0.0000  0.0000  0.01620 (19)  
P1  0.26355 (10)  0.45280 (13)  0.15910 (12)  0.0166 (2)  
H1  0.404 (6)  0.483 (6)  0.272 (7)  0.031 (11)*  
H2  0.308 (5)  0.566 (6)  −0.001 (5)  0.015 (8)*  
O1  0.2302 (3)  0.1773 (4)  0.1104 (3)  0.0188 (4)  
O2  0.1080 (3)  0.6010 (4)  0.2392 (3)  0.0190 (4)  
Atomic displacement parameters (Å^{2}) top  U^{11}  U^{22}  U^{33}  U^{12}  U^{13}  U^{23} 
Cu1  0.0181 (3)  0.0163 (3)  0.0151 (3)  −0.00162 (18)  0.00534 (18)  −0.00335 (18) 
P1  0.0177 (4)  0.0166 (4)  0.0164 (4)  −0.0015 (2)  0.0053 (3)  −0.0005 (2) 
O1  0.0191 (10)  0.0174 (9)  0.0203 (10)  −0.0001 (8)  0.0042 (8)  −0.0034 (8) 
O2  0.0259 (11)  0.0163 (9)  0.0161 (10)  0.0021 (8)  0.0074 (8)  0.0014 (8) 
Geometric parameters (Å, º) top
Cu1—O1  1.9454 (19)  P1—O2  1.521 (2) 
Cu1—O2^{i}  1.987 (2)  P1—H1  1.16 (4) 
Cu1—O2^{ii}  2.653 (2)  P1—H2  1.25 (3) 
P1—O1  1.516 (2)   
   
O1^{iii}—Cu1—O1  180.00 (17)  O1—P1—H2  111.1 (15) 
O1—Cu1—O2^{i}  89.88 (8)  O2—P1—H2  107.7 (16) 
O2^{iv}—Cu1—O2^{i}  180.00 (10)  H1—P1—H2  96 (3) 
O1—Cu1—O2^{ii}  91.76 (7)  P1—O1—Cu1  130.18 (12) 
O2^{i}—Cu1—O2^{ii}  82.78 (5)  P1—O2—Cu1^{v}  122.09 (12) 
O1—P1—O2  118.04 (12)  P1—O2—Cu1^{vi}  113.66 (10) 
O1—P1—H1  110.8 (17)  Cu1^{v}—O2—Cu1^{vi}  124.25 (9) 
O2—P1—H1  111 (2)   
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) x, y−1, z; (iii) −x, −y, −z; (iv) x, −y+1/2, z−1/2; (v) −x, y+1/2, −z+1/2; (vi) x, y+1, z. 
Hydrogenbond geometry (Å, º) top
D—H···A  D—H  H···A  D···A  D—H···A 
P1—H1···O1^{vii}  1.16 (4)  2.76 (4)  2.952 (2)  88 (2) 
P1—H2···O1^{iv}  1.25 (3)  2.74 (3)  3.472 (2)  116.0 (19) 
P1—H2···O2^{viii}  1.25 (3)  2.68 (3)  3.597 (2)  129 (2) 
P1—H1···O1^{ix}  1.16 (4)  2.82 (4)  3.905 (2)  155 (3) 
Symmetry codes: (iv) x, −y+1/2, z−1/2; (vii) x, −y+1/2, z+1/2; (viii) x, −y+3/2, z−1/2; (ix) −x+1, y+1/2, −z+1/2. 
Crystal data top
Cu(H_{2}PO_{2})_{2}  F(000) = 190 
M_{r} = 193.51  D_{x} = 2.729 Mg m^{−}^{3} 
Monoclinic, P2_{1}/c  Mo Kα radiation, λ = 0.71073 Å 
a = 7.2079 (3) Å  Cell parameters from 1117 reflections 
b = 5.3216 (1) Å  θ = 2.9–29.1° 
c = 6.2121 (2) Å  µ = 5.21 mm^{−}^{1} 
β = 98.709 (2)°  T = 100 K 
V = 235.53 (1) Å^{3}  Prism, blue 
Z = 2  0.19 × 0.11 × 0.03 mm 
Data collection top
Siemens SMART CCD diffractometer  612 independent reflections 
Radiation source: finefocus sealed tube  575 reflections with I > 2σ(I) 
Graphite monochromator  R_{int} = 0.033 
Detector resolution: 8.192 pixels mm^{1}  θ_{max} = 29.1°, θ_{min} = 2.9° 
ω scans  h = −7→9 
Absorption correction: analytical (XPREP; Siemens, 1995)  k = −7→7 
T_{min} = 0.518, T_{max} = 0.857  l = −8→8 
1689 measured reflections  
Refinement top
Refinement on F^{2}  Secondary atom site location: difference Fourier map 
Leastsquares matrix: full  Hydrogen site location: difference Fourier map 
R[F^{2} > 2σ(F^{2})] = 0.027  All Hatom parameters refined 
wR(F^{2}) = 0.062  w = 1/[σ^{2}(F_{o}^{2}) + (0.0249P)^{2} + 0.3031P] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
S = 1.18  (Δ/σ)_{max} < 0.001 
612 reflections  Δρ_{max} = 0.47 e Å^{−}^{3} 
43 parameters  Δρ_{min} = −0.42 e Å^{−}^{3} 
0 restraints  Extinction correction: SHELXL97, Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
Primary atom site location: structureinvariant direct methods  Extinction coefficient: 0.022 (4) 
Crystal data top
Cu(H_{2}PO_{2})_{2}  V = 235.53 (1) Å^{3} 
M_{r} = 193.51  Z = 2 
Monoclinic, P2_{1}/c  Mo Kα radiation 
a = 7.2079 (3) Å  µ = 5.21 mm^{−}^{1} 
b = 5.3216 (1) Å  T = 100 K 
c = 6.2121 (2) Å  0.19 × 0.11 × 0.03 mm 
β = 98.709 (2)°  
Data collection top
Siemens SMART CCD diffractometer  612 independent reflections 
Absorption correction: analytical (XPREP; Siemens, 1995)  575 reflections with I > 2σ(I) 
T_{min} = 0.518, T_{max} = 0.857  R_{int} = 0.033 
1689 measured reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.027  0 restraints 
wR(F^{2}) = 0.062  All Hatom parameters refined 
S = 1.18  Δρ_{max} = 0.47 e Å^{−}^{3} 
612 reflections  Δρ_{min} = −0.42 e Å^{−}^{3} 
43 parameters  
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. 
Refinement. Refinement of F^{2} against ALL reflections. The weighted Rfactor
wR and goodness of fit S are based on F^{2}, conventional
Rfactors R are based on F, with F set to zero for
negative F^{2}. The threshold expression of F^{2} >
σ(F^{2}) is used only for calculating Rfactors(gt) etc.
and is not relevant to the choice of reflections for refinement.
Rfactors based on F^{2} are statistically about twice as large
as those based on F, and R factors based on ALL data will be
even larger. 
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  
Cu1  0.0000  0.0000  0.0000  0.00775 (17)  
P1  0.26394 (9)  0.45455 (12)  0.15685 (11)  0.00832 (18)  
H1  0.412 (5)  0.477 (6)  0.271 (6)  0.014 (9)*  
H2  0.311 (5)  0.571 (6)  −0.009 (5)  0.005 (7)*  
O1  0.2317 (3)  0.1764 (3)  0.1092 (3)  0.0094 (4)  
O2  0.1069 (3)  0.6034 (3)  0.2369 (3)  0.0097 (4)  
Atomic displacement parameters (Å^{2}) top  U^{11}  U^{22}  U^{33}  U^{12}  U^{13}  U^{23} 
Cu1  0.0086 (3)  0.0078 (2)  0.0072 (2)  −0.00083 (15)  0.00234 (16)  −0.00176 (15) 
P1  0.0093 (3)  0.0080 (3)  0.0080 (3)  −0.0002 (2)  0.0026 (2)  −0.0002 (2) 
O1  0.0088 (9)  0.0096 (8)  0.0098 (9)  0.0004 (7)  0.0012 (7)  −0.0024 (7) 
O2  0.0134 (9)  0.0074 (8)  0.0089 (9)  0.0008 (7)  0.0040 (7)  −0.0002 (7) 
Geometric parameters (Å, º) top
Cu1—O1  1.9461 (18)  P1—O2  1.5252 (19) 
Cu1—O2^{i}  1.9872 (18)  P1—H1  1.20 (4) 
Cu1—O2^{ii}  2.6213 (18)  P1—H2  1.29 (3) 
P1—O1  1.5203 (18)   
   
O1^{iii}—Cu1—O1  180.00 (16)  O1—P1—H2  111.3 (14) 
O1—Cu1—O2^{i}  89.94 (7)  O2—P1—H2  108.0 (14) 
O2^{iv}—Cu1—O2^{i}  180.00 (9)  H1—P1—H2  96 (2) 
O1—Cu1—O2^{ii}  91.66 (7)  P1—O1—Cu1  129.45 (11) 
O2^{i}—Cu1—O2^{ii}  83.05 (5)  P1—O2—Cu1^{v}  121.58 (11) 
O1—P1—O2  118.03 (11)  P1—O2—Cu1^{vi}  113.87 (9) 
O1—P1—H1  108.0 (15)  Cu1^{v}—O2—Cu1^{vi}  124.54 (8) 
O2—P1—H1  113.4 (17)   
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) x, y−1, z; (iii) −x, −y, −z; (iv) x, −y+1/2, z−1/2; (v) −x, y+1/2, −z+1/2; (vi) x, y+1, z. 
Hydrogenbond geometry (Å, º) top
D—H···A  D—H  H···A  D···A  D—H···A 
P1—H1···O1^{vii}  1.20 (4)  2.76 (4)  2.9384 (19)  86.4 (19) 
P1—H2···O1^{iv}  1.29 (3)  2.70 (3)  3.4460 (19)  114.9 (18) 
P1—H2···O2^{viii}  1.29 (3)  2.64 (3)  3.5671 (19)  127.0 (19) 
P1—H1···O1^{ix}  1.20 (4)  2.77 (4)  3.8890 (19)  155 (2) 
Symmetry codes: (iv) x, −y+1/2, z−1/2; (vii) x, −y+1/2, z+1/2; (viii) x, −y+3/2, z−1/2; (ix) −x+1, y+1/2, −z+1/2. 
Crystal data top
Cu(H_{2}PO_{2})_{2}  D_{x} = 2.699 Mg m^{−}^{3} 
M_{r} = 193.51  Mo Kα radiation, λ = 0.71073 Å 
Orthorhombic, Pbca  Cell parameters from 1781 reflections 
a = 5.3259 (2) Å  θ = 2.9–29.1° 
b = 6.2720 (2) Å  µ = 5.15 mm^{−}^{1} 
c = 14.2590 (6) Å  T = 270 K 
V = 476.31 (3) Å^{3}  Prism, blue 
Z = 4  0.23 × 0.13 × 0.05 mm 
F(000) = 380  
Data collection top
Siemens SMART CCD diffractometer  631 independent reflections 
Radiation source: finefocus sealed tube  567 reflections with I > 2σ(I) 
Graphite monochromator  R_{int} = 0.029 
Detector resolution: 8.192 pixels mm^{1}  θ_{max} = 29.1°, θ_{min} = 2.9° 
ω scans  h = −7→7 
Absorption correction: analytical (XPREP; Siemens, 1995)  k = −7→8 
T_{min} = 0.420, T_{max} = 0.811  l = −17→19 
3218 measured reflections  
Refinement top
Refinement on F^{2}  Secondary atom site location: difference Fourier map 
Leastsquares matrix: full  Hydrogen site location: difference Fourier map 
R[F^{2} > 2σ(F^{2})] = 0.024  All Hatom parameters refined 
wR(F^{2}) = 0.059  w = 1/[σ^{2}(F_{o}^{2}) + (0.0226P)^{2} + 0.5274P] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
S = 1.27  (Δ/σ)_{max} < 0.001 
631 reflections  Δρ_{max} = 0.62 e Å^{−}^{3} 
43 parameters  Δρ_{min} = −0.30 e Å^{−}^{3} 
0 restraints  Extinction correction: SHELXL97, Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
Primary atom site location: structureinvariant direct methods  Extinction coefficient: 0.0090 (16) 
Crystal data top
Cu(H_{2}PO_{2})_{2}  V = 476.31 (3) Å^{3} 
M_{r} = 193.51  Z = 4 
Orthorhombic, Pbca  Mo Kα radiation 
a = 5.3259 (2) Å  µ = 5.15 mm^{−}^{1} 
b = 6.2720 (2) Å  T = 270 K 
c = 14.2590 (6) Å  0.23 × 0.13 × 0.05 mm 
Data collection top
Siemens SMART CCD diffractometer  631 independent reflections 
Absorption correction: analytical (XPREP; Siemens, 1995)  567 reflections with I > 2σ(I) 
T_{min} = 0.420, T_{max} = 0.811  R_{int} = 0.029 
3218 measured reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.024  0 restraints 
wR(F^{2}) = 0.059  All Hatom parameters refined 
S = 1.27  Δρ_{max} = 0.62 e Å^{−}^{3} 
631 reflections  Δρ_{min} = −0.30 e Å^{−}^{3} 
43 parameters  
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. 
Refinement. Refinement of F^{2} against ALL reflections. The weighted Rfactor
wR and goodness of fit S are based on F^{2}, conventional
Rfactors R are based on F, with F set to zero for
negative F^{2}. The threshold expression of F^{2} >
σ(F^{2}) is used only for calculating Rfactors(gt) etc.
and is not relevant to the choice of reflections for refinement.
Rfactors based on F^{2} are statistically about twice as large
as those based on F, and R factors based on ALL data will be
even larger. 
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  
Cu1  0.0000  0.0000  0.0000  0.01518 (16)  
P1  0.45389 (11)  0.11030 (10)  0.13084 (4)  0.01553 (17)  
H1  0.471 (5)  0.214 (5)  0.209 (2)  0.023 (8)*  
H2  0.571 (6)  −0.053 (5)  0.145 (2)  0.015 (7)*  
O1  0.1767 (3)  0.0678 (3)  0.11585 (11)  0.0183 (4)  
O2  0.5997 (3)  0.2201 (3)  0.05291 (12)  0.0174 (4)  
Atomic displacement parameters (Å^{2}) top  U^{11}  U^{22}  U^{33}  U^{12}  U^{13}  U^{23} 
Cu1  0.0157 (2)  0.0131 (2)  0.0168 (2)  −0.00277 (14)  −0.00103 (14)  0.00228 (15) 
P1  0.0158 (3)  0.0148 (3)  0.0160 (3)  0.0004 (2)  −0.0010 (2)  0.0023 (2) 
O1  0.0175 (8)  0.0190 (8)  0.0183 (8)  −0.0028 (6)  0.0010 (6)  0.0001 (6) 
O2  0.0143 (7)  0.0149 (8)  0.0231 (8)  0.0012 (6)  0.0016 (7)  0.0038 (6) 
Geometric parameters (Å, º) top
Cu1—O1  1.9483 (16)  P1—O2  1.5207 (17) 
Cu1—O2^{i}  1.9829 (16)  P1—H1  1.30 (3) 
Cu1—O2^{ii}  2.6496 (17)  P1—H2  1.21 (3) 
P1—O1  1.5151 (18)   
   
O1—Cu1—O1^{iii}  180.00 (5)  O1—P1—H2  112.0 (15) 
O1—Cu1—O2^{i}  90.00 (7)  O2—P1—H2  103.9 (14) 
O2^{iv}—Cu1—O2^{i}  180.00 (10)  H1—P1—H2  104.3 (19) 
O1—Cu1—O2^{ii}  91.92 (6)  P1—O1—Cu1  128.95 (10) 
O2^{i}—Cu1—O2^{ii}  82.10 (4)  P1—O2—Cu1^{v}  122.84 (10) 
O1—P1—O2  118.31 (10)  P1—O2—Cu1^{vi}  112.51 (8) 
O1—P1—H1  106.1 (12)  Cu1^{v}—O2—Cu1^{vi}  124.64 (7) 
O2—P1—H1  111.5 (14)   
Symmetry codes: (i) x−1/2, −y+1/2, −z; (ii) x−1, y, z; (iii) −x, −y, −z; (iv) −x+1/2, y−1/2, z; (v) x+1/2, −y+1/2, −z; (vi) x+1, y, z. 
Hydrogenbond geometry (Å, º) top
D—H···A  D—H  H···A  D···A  D—H···A 
P1—H1···O1^{vii}  1.30 (3)  2.70 (3)  2.9605 (17)  88.2 (16) 
P1—H2···O1^{iv}  1.21 (3)  2.75 (3)  3.4793 (17)  117.3 (19) 
P1—H2···O2^{viii}  1.21 (3)  2.61 (3)  3.5881 (18)  136.1 (19) 
P1—H1···O1^{ix}  1.30 (3)  2.88 (3)  3.8112 (17)  127.8 (19) 
Symmetry codes: (iv) −x+1/2, y−1/2, z; (vii) −x+1/2, y+1/2, z; (viii) −x+3/2, y−1/2, z; (ix) x+1/2, y, −z+1/2. 
Crystal data top
Cu(H_{2}PO_{2})_{2}  D_{x} = 2.732 Mg m^{−}^{3} 
M_{r} = 193.51  Mo Kα radiation, λ = 0.71073 Å 
Orthorhombic, Pbca  Cell parameters from 1900 reflections 
a = 5.3014 (2) Å  θ = 2.9–29.1° 
b = 6.2319 (2) Å  µ = 5.21 mm^{−}^{1} 
c = 14.2427 (2) Å  T = 100 K 
V = 470.55 (2) Å^{3}  Prism, blue 
Z = 4  0.23 × 0.13 × 0.05 mm 
F(000) = 380  
Data collection top
Siemens SMART CCD diffractometer  624 independent reflections 
Radiation source: finefocus sealed tube  606 reflections with I > 2σ(I) 
Graphite monochromator  R_{int} = 0.029 
Detector resolution: 8.192 pixels mm^{1}  θ_{max} = 29.1°, θ_{min} = 2.9° 
ω scans  h = −7→7 
Absorption correction: analytical (XPREP; Siemens, 1995)  k = −7→8 
T_{min} = 0.417, T_{max} = 0.809  l = −17→19 
2974 measured reflections  
Refinement top
Refinement on F^{2}  Secondary atom site location: difference Fourier map 
Leastsquares matrix: full  Hydrogen site location: difference Fourier map 
R[F^{2} > 2σ(F^{2})] = 0.028  All Hatom parameters refined 
wR(F^{2}) = 0.062  w = 1/[σ^{2}(F_{o}^{2}) + (0.0198P)^{2} + 1.149P] where P = (F_{o}^{2} + 2F_{c}^{2})/3 
S = 1.29  (Δ/σ)_{max} < 0.001 
624 reflections  Δρ_{max} = 0.68 e Å^{−}^{3} 
43 parameters  Δρ_{min} = −0.33 e Å^{−}^{3} 
0 restraints  Extinction correction: SHELXL97, Fc^{*}=kFc[1+0.001xFc^{2}λ^{3}/sin(2θ)]^{1/4} 
Primary atom site location: structureinvariant direct methods  Extinction coefficient: 0.0101 (17) 
Crystal data top
Cu(H_{2}PO_{2})_{2}  V = 470.55 (2) Å^{3} 
M_{r} = 193.51  Z = 4 
Orthorhombic, Pbca  Mo Kα radiation 
a = 5.3014 (2) Å  µ = 5.21 mm^{−}^{1} 
b = 6.2319 (2) Å  T = 100 K 
c = 14.2427 (2) Å  0.23 × 0.13 × 0.05 mm 
Data collection top
Siemens SMART CCD diffractometer  624 independent reflections 
Absorption correction: analytical (XPREP; Siemens, 1995)  606 reflections with I > 2σ(I) 
T_{min} = 0.417, T_{max} = 0.809  R_{int} = 0.029 
2974 measured reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.028  0 restraints 
wR(F^{2}) = 0.062  All Hatom parameters refined 
S = 1.29  Δρ_{max} = 0.68 e Å^{−}^{3} 
624 reflections  Δρ_{min} = −0.33 e Å^{−}^{3} 
43 parameters  
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. 
Refinement. Refinement of F^{2} against ALL reflections. The weighted Rfactor
wR and goodness of fit S are based on F^{2}, conventional
Rfactors R are based on F, with F set to zero for
negative F^{2}. The threshold expression of F^{2} >
σ(F^{2}) is used only for calculating Rfactors(gt) etc.
and is not relevant to the choice of reflections for refinement.
Rfactors based on F^{2} are statistically about twice as large
as those based on F, and R factors based on ALL data will be
even larger. 
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  
Cu1  0.0000  0.0000  0.0000  0.00728 (17)  
P1  0.45577 (12)  0.10826 (10)  0.13094 (5)  0.00789 (18)  
H1  0.480 (6)  0.214 (6)  0.211 (2)  0.009 (8)*  
H2  0.573 (7)  −0.066 (5)  0.145 (2)  0.008 (8)*  
O1  0.1756 (3)  0.0667 (3)  0.11692 (12)  0.0095 (4)  
O2  0.6015 (3)  0.2177 (3)  0.05204 (13)  0.0091 (4)  
Atomic displacement parameters (Å^{2}) top  U^{11}  U^{22}  U^{33}  U^{12}  U^{13}  U^{23} 
Cu1  0.0077 (2)  0.0066 (2)  0.0075 (2)  −0.00120 (15)  −0.00048 (14)  0.00108 (16) 
P1  0.0081 (3)  0.0079 (3)  0.0076 (3)  0.0004 (2)  −0.0003 (2)  0.0009 (2) 
O1  0.0093 (8)  0.0098 (8)  0.0094 (8)  −0.0011 (6)  0.0007 (6)  −0.0007 (7) 
O2  0.0073 (8)  0.0091 (8)  0.0108 (8)  0.0012 (7)  0.0004 (7)  0.0009 (7) 
Geometric parameters (Å, º) top
Cu1—O1  1.9526 (18)  P1—O2  1.5247 (19) 
Cu1—O2^{i}  1.9835 (18)  P1—H1  1.32 (3) 
Cu1—O2^{ii}  2.6178 (18)  P1—H2  1.27 (3) 
P1—O1  1.5209 (19)   
   
O1—Cu1—O1^{iii}  180.00 (5)  O1—P1—H2  110.6 (16) 
O1—Cu1—O2^{i}  90.03 (7)  O2—P1—H2  104.4 (16) 
O2^{iv}—Cu1—O2^{i}  180.00 (10)  H1—P1—H2  104 (2) 
O1—Cu1—O2^{ii}  91.89 (7)  P1—O1—Cu1  127.87 (11) 
O2^{i}—Cu1—O2^{ii}  82.25 (5)  P1—O2—Cu1^{v}  122.32 (11) 
O1—P1—O2  118.31 (10)  P1—O2—Cu1^{vi}  112.70 (9) 
O1—P1—H1  107.0 (13)  Cu1^{v}—O2—Cu1^{vi}  124.94 (8) 
O2—P1—H1  111.3 (15)   
Symmetry codes: (i) x−1/2, −y+1/2, −z; (ii) x−1, y, z; (iii) −x, −y, −z; (iv) −x+1/2, y−1/2, z; (v) x+1/2, −y+1/2, −z; (vi) x+1, y, z. 
Hydrogenbond geometry (Å, º) top
D—H···A  D—H  H···A  D···A  D—H···A 
P1—H1···O1^{vii}  1.32 (3)  2.70 (3)  2.9475 (19)  87.1 (16) 
P1—H2···O1^{iv}  1.27 (3)  2.67 (3)  3.4517 (19)  118 (2) 
P1—H2···O2^{viii}  1.27 (3)  2.56 (3)  3.5632 (19)  135 (2) 
P1—H1···O1^{ix}  1.32 (3)  2.82 (3)  3.7843 (19)  129 (2) 
Symmetry codes: (iv) −x+1/2, y−1/2, z; (vii) −x+1/2, y+1/2, z; (viii) −x+3/2, y−1/2, z; (ix) x+1/2, y, −z+1/2. 
Crystal data top
Cu(H_{2}PO_{2})_{2}  D_{x} = 2.472 Mg m^{−}^{3} 
M_{r} = 193.51  Mo Kα radiation, λ = 0.71073 Å 
Orthorhombic, Pmma  Cell parameters from 24 reflections 
a = 6.6738 (6) Å  θ = 10–15° 
b = 5.4133 (5) Å  µ = 4.72 mm^{−}^{1} 
c = 7.1954 (6) Å  T = 270 K 
V = 259.95 (4) Å^{3}  Needle, blue 
Z = 2  0.52 × 0.03 × 0.01 mm 
F(000) = 190  
Data collection top
EnrafNonius CAD4 diffractometer  341 reflections with I > 2σ(I) 
Radiation source: finefocus sealed tube  R_{int} = 0.042 
Graphite monochromator  θ_{max} = 29.1°, θ_{min} = 2.8° 
2θ/θ scans  h = −1→8 
Absorption correction: analytical (XPREP; Siemens, 1995)  k = −1→7 
T_{min} = 0.501, T_{max} = 0.605  l = −1→9 
939 measured reflections  3 standard reflections every 60 min 
405 independent reflections  intensity decay: none 
Refinement top
Refinement on F^{2}  Primary atom site location: structureinvariant direct methods 
Leastsquares matrix: full  Secondary atom site location: difference Fourier map 
R[F^{2} > 2σ(F^{2})] = 0.033  Hydrogen site location: difference Fourier map 
wR(F^{2}) = 0.045  H atoms treated by a mixture of independent and constrained refinement 
S = 1.10  w = 1/[σ^{2}(F_{o}^{2})] 
405 reflections  (Δ/σ)_{max} < 0.001 
27 parameters  Δρ_{max} = 0.42 e Å^{−}^{3} 
0 restraints  Δρ_{min} = −0.51 e Å^{−}^{3} 
Crystal data top
Cu(H_{2}PO_{2})_{2}  V = 259.95 (4) Å^{3} 
M_{r} = 193.51  Z = 2 
Orthorhombic, Pmma  Mo Kα radiation 
a = 6.6738 (6) Å  µ = 4.72 mm^{−}^{1} 
b = 5.4133 (5) Å  T = 270 K 
c = 7.1954 (6) Å  0.52 × 0.03 × 0.01 mm 
Data collection top
EnrafNonius CAD4 diffractometer  341 reflections with I > 2σ(I) 
Absorption correction: analytical (XPREP; Siemens, 1995)  R_{int} = 0.042 
T_{min} = 0.501, T_{max} = 0.605  3 standard reflections every 60 min 
939 measured reflections  intensity decay: none 
405 independent reflections  
Refinement top
R[F^{2} > 2σ(F^{2})] = 0.033  0 restraints 
wR(F^{2}) = 0.045  H atoms treated by a mixture of independent and constrained refinement 
S = 1.10  Δρ_{max} = 0.42 e Å^{−}^{3} 
405 reflections  Δρ_{min} = −0.51 e Å^{−}^{3} 
27 parameters  
Special details top
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes)
are estimated using the full covariance matrix. The cell e.s.d.'s are taken
into account individually in the estimation of e.s.d.'s in distances, angles
and torsion angles; correlations between e.s.d.'s in cell parameters are only
used when they are defined by crystal symmetry. An approximate (isotropic)
treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s.
planes. 
Refinement. Refinement of F^{2} against ALL reflections. The weighted Rfactor
wR and goodness of fit S are based on F^{2}, conventional
Rfactors R are based on F, with F set to zero for
negative F^{2}. The threshold expression of F^{2} >
σ(F^{2}) is used only for calculating Rfactors(gt) etc.
and is not relevant to the choice of reflections for refinement.
Rfactors based on F^{2} are statistically about twice as large
as those based on F, and R factors based on ALL data will be
even larger. 
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å^{2}) top  x  y  z  U_{iso}*/U_{eq}  Occ. (<1) 
Cu1  0.0000  0.5000  0.0000  0.01590 (16)  
P1  0.2500  0.0000  −0.1476 (2)  0.0364 (4)  
H1A  0.414 (5)  0.0000  −0.259 (3)  0.044*  0.50 
H1B  0.086 (5)  0.0000  −0.259 (3)  0.044*  0.50 
O1  0.2500  0.2382 (4)  −0.0362 (3)  0.0340 (7)  
P2  0.2500  0.5000  0.36694 (19)  0.0310 (4)  
H2A  0.2500  0.292 (5)  0.484 (3)  0.037*  0.50 
H2B  0.2500  0.708 (5)  0.484 (3)  0.037*  0.50 
O2  0.0560 (3)  0.5000  0.2659 (3)  0.0246 (6)  
Atomic displacement parameters (Å^{2}) top  U^{11}  U^{22}  U^{33}  U^{12}  U^{13}  U^{23} 
Cu1  0.0104 (3)  0.0149 (2)  0.0224 (3)  0.000  0.0008 (3)  0.000 
P1  0.0614 (13)  0.0170 (6)  0.0308 (8)  0.000  0.000  0.000 
O1  0.0481 (18)  0.0155 (11)  0.0385 (16)  0.000  0.000  −0.0053 (12) 
P2  0.0165 (8)  0.0544 (9)  0.0220 (7)  0.000  0.000  0.000 
O2  0.0101 (12)  0.0419 (15)  0.0219 (12)  0.000  −0.0021 (10)  0.000 
Geometric parameters (Å, º) top
Cu1—O1  2.2046 (14)  P1—H1A  1.3585 
Cu1—O2  1.949 (2)  P2—O2  1.485 (2) 
P1—O1  1.518 (2)  P2—H2A  1.4058 
   
O1—Cu1—O1^{i}  80.01 (9)  O1—P1—H1A  108.2 
O2—Cu1—O1  88.33 (8)  O1—P1—H1B  108.2 
O2—Cu1—O1^{i}  88.33 (8)  H1A—P1—H1B  107.4 
O2—Cu1—O2^{ii}  180.0  O2—P2—O2^{i}  121.4 (2) 
O1^{i}—Cu1—O1^{iii}  180.0  O2—P2—H2A  107.0 
O2—Cu1—Cu1^{i}  78.95 (7)  O2—P2—H2B  107.0 
O2^{ii}—Cu1—Cu1^{i}  101.05 (7)  H2A—P2—H2B  106.7 
O1^{i}—Cu1—Cu1^{i}  40.82 (4)  P1—O1—Cu1  127.47 (6) 
O1^{iii}—Cu1—Cu1^{i}  139.18 (4)  P2—O2—Cu1  130.37 (15) 
O1—Cu1—Cu1^{i}  40.82 (4)  Cu1—O1—Cu1^{i}  98.36 (9) 
O1—P1—O1^{iv}  116.3 (2)   
Symmetry codes: (i) −x+1/2, −y+1, z; (ii) −x, −y+1, −z; (iii) x−1/2, y, −z; (iv) −x+1/2, −y, z. 
Hydrogenbond geometry (Å, º) top
D—H···A  D—H  H···A  D···A  D—H···A 
P1—H1A···O2^{v}  1.36  2.87  3.4958 (15)  106 
P1—H1A···O2^{vi}  1.36  2.87  3.4958 (15)  106 
P2—H2A···O2^{vii}  1.41  2.95  3.339 (2)  93 
P2—H2B···O2^{viii}  1.41  2.95  3.339 (2)  93 
Symmetry codes: (v) x+1/2, −y, −z; (vi) x+1/2, −y+1, −z; (vii) x+1/2, −y+1, −z+1; (viii) −x, y, −z+1. 
Experimental details
 (alpha270)  (alpha100)  (beta270)  (beta100) 
Crystal data 
Chemical formula  Cu(H_{2}PO_{2})_{2}  Cu(H_{2}PO_{2})_{2}  Cu(H_{2}PO_{2})_{2}  Cu(H_{2}PO_{2})_{2} 
M_{r}  193.51  193.51  193.51  193.51 
Crystal system, space group  Monoclinic, P2_{1}/c  Monoclinic, P2_{1}/c  Orthorhombic, Pbca  Orthorhombic, Pbca 
Temperature (K)  270  100  270  100 
a, b, c (Å)  7.2186 (1), 5.3462 (2), 6.2521 (3)  7.2079 (3), 5.3216 (1), 6.2121 (2)  5.3259 (2), 6.2720 (2), 14.2590 (6)  5.3014 (2), 6.2319 (2), 14.2427 (2) 
α, β, γ (°)  90, 98.8352 (11), 90  90, 98.709 (2), 90  90, 90, 90  90, 90, 90 
V (Å^{3})  238.42 (2)  235.53 (1)  476.31 (3)  470.55 (2) 
Z  2  2  4  4 
Radiation type  Mo Kα  Mo Kα  Mo Kα  Mo Kα 
µ (mm^{−}^{1})  5.14  5.21  5.15  5.21 
Crystal size (mm)  0.19 × 0.11 × 0.03  0.19 × 0.11 × 0.03  0.23 × 0.13 × 0.05  0.23 × 0.13 × 0.05 

Data collection 
Diffractometer  Siemens SMART CCD diffractometer  Siemens SMART CCD diffractometer  Siemens SMART CCD diffractometer  Siemens SMART CCD diffractometer 
Absorption correction  Analytical (XPREP; Siemens, 1995)  Analytical (XPREP; Siemens, 1995)  Analytical (XPREP; Siemens, 1995)  Analytical (XPREP; Siemens, 1995) 
T_{min}, T_{max}  0.521, 0.859  0.518, 0.857  0.420, 0.811  0.417, 0.809 
No. of measured, independent and observed [I > 2σ(I)] reflections  1697, 620, 578  1689, 612, 575  3218, 631, 567  2974, 624, 606 
R_{int}  0.034  0.033  0.029  0.029 
(sin θ/λ)_{max} (Å^{−}^{1})  0.684  0.683  0.685  0.685 

Refinement 
R[F^{2} > 2σ(F^{2})], wR(F^{2}), S  0.031, 0.068, 1.18  0.027, 0.062, 1.18  0.024, 0.059, 1.27  0.028, 0.062, 1.29 
No. of reflections  620  612  631  624 
No. of parameters  43  43  43  43 
Hatom treatment  All Hatom parameters refined  All Hatom parameters refined  All Hatom parameters refined  All Hatom parameters refined 
Δρ_{max}, Δρ_{min} (e Å^{−}^{3})  0.47, −0.36  0.47, −0.42  0.62, −0.30  0.68, −0.33 
 (gamma270) 
Crystal data 
Chemical formula  Cu(H_{2}PO_{2})_{2} 
M_{r}  193.51 
Crystal system, space group  Orthorhombic, Pmma 
Temperature (K)  270 
a, b, c (Å)  6.6738 (6), 5.4133 (5), 7.1954 (6) 
α, β, γ (°)  90, 90, 90 
V (Å^{3})  259.95 (4) 
Z  2 
Radiation type  Mo Kα 
µ (mm^{−}^{1})  4.72 
Crystal size (mm)  0.52 × 0.03 × 0.01 

Data collection 
Diffractometer  EnrafNonius CAD4 diffractometer 
Absorption correction  Analytical (XPREP; Siemens, 1995) 
T_{min}, T_{max}  0.501, 0.605 
No. of measured, independent and observed [I > 2σ(I)] reflections  939, 405, 341 
R_{int}  0.042 
(sin θ/λ)_{max} (Å^{−}^{1})  0.684 

Refinement 
R[F^{2} > 2σ(F^{2})], wR(F^{2}), S  0.033, 0.045, 1.10 
No. of reflections  405 
No. of parameters  27 
Hatom treatment  H atoms treated by a mixture of independent and constrained refinement 
Δρ_{max}, Δρ_{min} (e Å^{−}^{3})  0.42, −0.51 
Selected geometric parameters (Å, º) for (alpha270) topCu1—O1  1.9454 (19)  P1—O1  1.516 (2) 
Cu1—O2^{i}  1.987 (2)  P1—O2  1.521 (2) 
Cu1—O2^{ii}  2.653 (2)   
   
O1—Cu1—O2^{i}  89.88 (8)  P1—O1—Cu1  130.18 (12) 
O1—Cu1—O2^{ii}  91.76 (7)  P1—O2—Cu1^{iii}  122.09 (12) 
O2^{i}—Cu1—O2^{ii}  82.78 (5)  P1—O2—Cu1^{iv}  113.66 (10) 
O1—P1—O2  118.04 (12)  Cu1^{iii}—O2—Cu1^{iv}  124.25 (9) 
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) x, y−1, z; (iii) −x, y+1/2, −z+1/2; (iv) x, y+1, z. 
Selected geometric parameters (Å, º) for (alpha100) topCu1—O1  1.9461 (18)  P1—O1  1.5203 (18) 
Cu1—O2^{i}  1.9872 (18)  P1—O2  1.5252 (19) 
Cu1—O2^{ii}  2.6213 (18)   
   
O1—Cu1—O2^{i}  89.94 (7)  P1—O1—Cu1  129.45 (11) 
O1—Cu1—O2^{ii}  91.66 (7)  P1—O2—Cu1^{iii}  121.58 (11) 
O2^{i}—Cu1—O2^{ii}  83.05 (5)  P1—O2—Cu1^{iv}  113.87 (9) 
O1—P1—O2  118.03 (11)  Cu1^{iii}—O2—Cu1^{iv}  124.54 (8) 
Symmetry codes: (i) −x, y−1/2, −z+1/2; (ii) x, y−1, z; (iii) −x, y+1/2, −z+1/2; (iv) x, y+1, z. 
Selected geometric parameters (Å, º) for (beta270) topCu1—O1  1.9483 (16)  P1—O1  1.5151 (18) 
Cu1—O2^{i}  1.9829 (16)  P1—O2  1.5207 (17) 
Cu1—O2^{ii}  2.6496 (17)   
   
O1—Cu1—O2^{i}  90.00 (7)  P1—O1—Cu1  128.95 (10) 
O1—Cu1—O2^{ii}  91.92 (6)  P1—O2—Cu1^{iii}  122.84 (10) 
O2^{i}—Cu1—O2^{ii}  82.10 (4)  P1—O2—Cu1^{iv}  112.51 (8) 
O1—P1—O2  118.31 (10)  Cu1^{iii}—O2—Cu1^{iv}  124.64 (7) 
Symmetry codes: (i) x−1/2, −y+1/2, −z; (ii) x−1, y, z; (iii) x+1/2, −y+1/2, −z; (iv) x+1, y, z. 
Selected geometric parameters (Å, º) for (beta100) topCu1—O1  1.9526 (18)  P1—O1  1.5209 (19) 
Cu1—O2^{i}  1.9835 (18)  P1—O2  1.5247 (19) 
Cu1—O2^{ii}  2.6178 (18)   
   
O1—Cu1—O2^{i}  90.03 (7)  P1—O1—Cu1  127.87 (11) 
O1—Cu1—O2^{ii}  91.89 (7)  P1—O2—Cu1^{iii}  122.32 (11) 
O2^{i}—Cu1—O2^{ii}  82.25 (5)  P1—O2—Cu1^{iv}  112.70 (9) 
O1—P1—O2  118.31 (10)  Cu1^{iii}—O2—Cu1^{iv}  124.94 (8) 
Symmetry codes: (i) x−1/2, −y+1/2, −z; (ii) x−1, y, z; (iii) x+1/2, −y+1/2, −z; (iv) x+1, y, z. 
Selected geometric parameters (Å, º) for (gamma270) topCu1—O1  2.2046 (14)  P1—O1  1.518 (2) 
Cu1—O2  1.949 (2)  P2—O2  1.485 (2) 
   
O1—Cu1—O1^{i}  80.01 (9)  O2—P2—O2^{i}  121.4 (2) 
O2—Cu1—O1  88.33 (8)  P1—O1—Cu1  127.47 (6) 
O2—Cu1—O1^{i}  88.33 (8)  P2—O2—Cu1  130.37 (15) 
O1—P1—O1^{ii}  116.3 (2)  Cu1—O1—Cu1^{i}  98.36 (9) 
Symmetry codes: (i) −x+1/2, −y+1, z; (ii) −x+1/2, −y, z. 
The first structural studies of ammonium hypophosphite and hexahydrates of cobalt, nickel and magnesium hypophosphites were reported 65 years ago (Zachariasen & Mooney, 1934; Ferrari & Colla, 1937). The crystal structures of hypophosphites of anhydrous calcium (Wyckoff, 1964), zinc (Tanner et al., 1997), germanium (Weakley, 1983), erbium (Aslanov et al., 1975), uranium (Tanner et al., 1992), and a urea complex of copper (Naumov et al., 2001) are known. No structural data for pure copper(II) hypophosphite have yet been reported. Since precise data on the structure of copper(II) hypophosphite are very important for understanding the mechanism of the decomposition of this salt, which finds numerous practical applications (Lomovsky & Boldyrev, 1994), we have undertaken its singlecrystal Xray structure determination.
Copper(II) hypophosphite is very unstable, therefore low temperatures were required both for crystal growth and data collection. A special device for crystal growth, based on the Oxford Cryosystems Cryostream cooler (Naumov, 2001), allowed us to obtain crystals of quality and dimensions acceptable for singlecrystal diffraction analysis. Using a SMART CCD diffractometer has allowed us to decrease the time of data collection to 6 h without loss of crystal quality and to collect data at several different temperatures for the same crystal.
Our studies have shown copper(II) hypophosphite to exist as three polymorphs, which we have called the α, β and γpolymorphs. Crystals of all three polymorphs grew from the same solution simultaneously. The α and βpolymorphs have the same rhombic plate habit and can be distinguished only by structural analysis. The γpolymorph grew as needles and could be recognized visually. Several powder patterns of copper hypophosphite have been reported (Balema et al., 1988; Brun & Dumail, 1971; Michailow et al., 1980), which are different and unindexed. The calculated powder pattern of the needle crystal of the γpolymorph is in good agreement with the powder pattern published by Brun & Dumail (1971). The calculated powder pattern of the rhombic plate crystal of the first discovered αpolymorph does not completely describe the known powder pattern (Balema et al., 1988). The method of preparation used in the present study excludes the formation of different substances. We successfully undertook a search for additional phases and found two polymorphs of the rhombic plate crystal. The calculated powder patterns of the rhombic plate crystal of the α and βpolymorphs are in good agreement with the powder patterns published by Balema et al. (1988) and Michailow et al. (1980). The crystal structures of the α and βpolymorphs differ from those previously reported for other anhydrous hypophosphites, such as Zn(H_{2}PO_{2})_{2} (Tanner et al., 1997) and Ca(H_{2}PO_{2})_{2} (Wyckoff, 1964). It is worth mentioning, that the γpolymorph is isostructural with zinc hypophosphite.
The geometry of the hypophosphite anion in all three polymorphs is very close to the idealized one, with point symmetry mm2. The average geometric parameters of the hypophosphite anion in anhydrous Cu(H_{2}PO_{2})_{2} [P—O 1.51 (2) Å and O—P—O 118.3 (17)°] are in good agreement with those of the urea complex of copper hypophosphite [P—O 1.515 (5) Å and O—P—O 117.84 (8)°; Naumov et al., 2001]. Despite having different space groups, the structures of the α and βpolymorphs are very similar. The coordination of the Cu atoms and of the hypophospite anions in the structures are also identical. Each Cu atom is coordinated by six O atoms of six hypophosphite anions, forming a tetragonal bipyramid [αpolymorph (270 K): four short, 1.9454 (19) (× 2) and 1.987 (2) Å (× 2), and two long, 2.653 (2) Å (× 2); βpolymorph (270 K): four short, 1.9483 (16) (× 2) and 1.9829 (16) Å (× 2), and two long, 2.6496 (17) Å (× 2)]. The short Cu—O bonds do not alter during cooling (see Tables 1 and 3). Each hypophosphite anion is coordinated to three Cu atoms. The geometry of the hypophosphite anions (P—O distances and O—P—O angles) does not change during cooling (see Tables 1 and 3). The hypophosphite anions and Cu cations form polymeric layers in the (100) (Fig. 1) and the (001) planes (Fig. 2) for the α and βpolymorphs, respectively. The copper cations form a distorted square pattern, with equal Cu···Cu distances [4.1131 (1) Å at 270 K and 4.0899 (1) Å at 100 K in the αpolymorph; 4.1141 (1) Å at 270 K and 4.0909 (1) Å at 100 K in the βpolymorph]. The layers, which are identical in the α and βpolymorphs, are stacked in the third dimension in different ways. In the αpolymorph, they align identically above each other [AAAA] (Fig. 3) and in the βpolymorph they align as [ABAB] (Fig. 4), i.e. not vertically stacked, and it is this alternate stacking pattern which generates the cell edge doubling in the direction perpendicular to the layers [2a (I) ≈ c (II)].
The coordination of the Cu atoms and hypophospite anions in the γpolymorph is quite different to that in the α and βpolymorphs. Each Cu atom is coordinated by six O atoms of six hypophosphite anions, forming a tetragonal bipyramid [two short, 1.949 (2) Å (× 2), and four long, 2.2046 (14) Å (× 4) at 270 K]. There are two symmetryindependent hypophosphite anions in the structure of the γpolymorph. The first is coordinated to two Cu atoms, while the second is coordinated to four Cu atoms. The hypophosphite anions and Cu cations form polymeric layers in the (001) planes (Fig. 5). The copper cations form a rectangle pattern with different Cu···Cu distances [3.3369 (3) Å and 5.4133 (5) Å]. The layers are aligned above each other (Fig. 6).
The P and O atoms of the γpolymorph are rather anisotropic compared with the 270 K data for the α and βpolymorphs. This can be explained by the existence of vibration freedom along the [100] and [010] directions of the coordinated hypophosphite anion and less closed packing. The calculated densities are 2.696, 2.699 and 2.472 Mg m^{3} at 270 K for the α, β and γpolymorphs, respectively.
In all three polymorphs, separate layers are linked by van der Waals interactions. The shortest H···H distances between layers are 2.86 (5), 2.55 (4) and 2.67 (3) Å at 270 K for the α, β and γpolymorphs, respectively.
On cooling to 100 K, the structure of the αpolymorph contracted anisotropically. The direction of minimum contraction [0.105 (2)%; axis 1 of the strain tensor in Fig. 1] is close to the normal to the planes of the polymeric layers. The direction of medium contraction [0.460 (4)%; axis 2 of the strain tensor in Fig. 1] coincided with the crystallographic b axis. The direction of maximum contraction [0.649 (4)%; axis 3 of the strain tensor in Fig. 1] is close to the crystallographic c axis.
On cooling to 100 K, the structure of the βpolymorph contracted anisotropically. The direction of minimum contraction [0.114 (4)%; axis 1 of the strain tensor in Fig. 2] coincided with the crystallographic c axis and was normal to the planes of the polymeric layers. The direction of medium contraction [0.460 (4)%; axis 2 of the strain tensor in Fig. 2] coincided with the crystallographic a axis. The direction of maximum contraction [0.639 (2)%; axis 3 of the strain tensor in Fig. 2] coincided with the crystallographic b axis.
The contractions on cooling in the α and βpolymorphs are very similar. The direction of minimum contraction can be correlated with the repulsive H···H interactions between different layers. The directions of medium and maximum contraction in the layer can be correlated with the contraction of the long Cu1—O2^{ii} distances on cooling [symmetry codes: (ii) x, y  1, z, for (I); x  1, y, z, for (II)].
On cooling to 100 K, the crystal of the γpolymorph cracked at about 120 K.